Mobile generator for supplying power to the on-board power supply system from ground, especially the on-board power supply system of a parked aircraft

ABSTRACT

Where the underground electrical power supply in an airport apron area is not sufficiently powerful for temporarily parked aircraft, or even does not exist at all, a conventional diesel-powered electrodynamic generator is, inventively replaced by a mobile generator ( 1 ) having an electrochemical cell ( 3 ) as the source of the electrical power for a temporary external feed into the on-board power supply system. The cell ( 3 ) may be a rechargeable lithium battery; however, it is preferably a fuel cell ( 3 ) with all the additional devices for its autonomous operation is located in a self-propelled or towed trolley ( 2 ).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a generator for applying ground power to the on-board power supply system of in particular, a parked aircraft.

2. Discussion of the Prior Art

One such generator is known from DE 83 10 749 U, in the form of a diesel-electric set. Where no underground wiring, which may in any case be subject to fees, can be accessed, the generator is moved to an aircraft that is parked for brief servicing, and is externally connected to the on-board power supply system of this aircraft via a plug interface located under the cockpit. This is the situation, in particular, at relatively small airports, or else in the case of large installations this situation occurs widely in the outer positions of the apron areas which are remote from the gates. This external electrical power supply makes it possible to dispense with the operation of the main engines or auxiliary power units for driving the on-board generators when in the parked position, thus avoiding the environmental contamination which results from this.

However, a diesel-electric set such as of this type also produces exhaust gases and noise. The emission from a plurality of diesel generators which are operated at the same time, particularly at night, on an airfield quickly reaches and exceeds the ever stricter limit-value requirements for environmental protection. Furthermore, their operation is becoming increasingly uneconomical, in terms of reasonable energy efficiency, and because of rising fuel costs.

SUMMARY OF THE INVENTION

The invention is therefore based on the technical problem of specifying a generator of this generic type, whose operating characteristics are designed for future compatibility.

According to the invention, this object is achieved by a generator which is designed as a mobile generator that has a towed or self-propelled trolley having at least one electrochemical cell.

Accordingly, the external mobile electrical supply for the parked aircraft is no longer provided dynamo-electrically by means of diesel power, but from the at least one electrochemical cell as a mobile generator, because this does not create any environmental contamination when in the parked position on the apron.

This mobile cell may be a rechargeable battery which is equipped with a standardized electromechanical interface and which is moved back to the equipment area after being used, where it is recharged again from a stationary power supply system, during a rest cycle. In particular, a lithium-polymer rechargeable battery or a lithium-ion rechargeable battery may be used for this purpose.

As an alternative to a rechargeable battery, extremely high-capacitance capacitors (for example electrical energy storage units, EESUs) may be used.

The mobile generator designed according to the invention is, however, preferably a fuel cell which can be operated autonomously, that is to say it is physically equipped with the required sets such as, in particular, an active substance supply and a voltage converter, since this system has considerably higher gravimetric and volumetric energy densities, in comparison to rechargeable batteries. It generates electrical power in a closed system, without any hazardous emissions and without noise. The efficiencies achieved using fuel cells with an operational capability are already considerably higher than those considered intrinsically for petrol or diesel engines, that is to say even without considering the losses which additionally occur when driving them by dynamo-electrical generators; and the present development work relating to fuel cells, which is being progressed everywhere, is expected to allow significant further improvements in terms of efficiency, power density, life etc., as well as power increases.

In particular, a stack of the hydrogen-powered PEM-FC type (polymer electrolyte membrane fuel cell) is suitable for use as a fuel cell for the mobile generator according to the invention, whose plastic membrane acts as an electrolyte, because its handling is not complicated, and its power output can be influenced with a wide dynamic range. The hydrogen as the fuel for operation of this fuel cell can be stored in liquid form in a cryogenic tank, or else has compressed gas in cylinders, in metal-hydride stores or in nanostores such as carbon nanotubes, carbon nanofibers or so-called MOFs (metal organic frameworks, nanocubes). The oxidant is liquefied or compressed oxygen, stored cryogenically or in cylinders. If there is no requirement for high-purity oxygen, and air oxygen can instead be used for the chemical reaction, the oxygen stores in the mobile generator can be replaced by an air compressor or even by an electrical turbocharger, which in contrast is physically much lighter.

In order to replenish the active substances (fuel and oxygen) for the fuel cell and for servicing tasks such as replacement of the fuel cell itself, the mobile generator does not need to leave the safety area for example of the fuel storage depots at an airport, and tasks such as these can be carried out without any problems in situ by the technical servicing personnel, after instruction. In order to be completely autonomous, an installation for obtaining the active substances to be stored for operation of a fuel cell, that is to say for example for the PEM-FC of high-purity hydrogen and oxygen by means of electrolysis, can be operated in that area, with subsequent liquefaction of the gases by compression or using the Linde process for cryo-storage, or by compression of the gases for storage in the pressurized cylinders. The hydrogen for operation of the PEM-FC may, however, also be obtained in the generator itself by means of a reformer from, for example, methane, methanol or ethanol that is also carried. The generator operation according to the invention is in any case entirely ecological, because the active substances that are used can be obtained regeneratively.

On the other hand, fuel cells that have been developed from the PEM-FC, of the DM-FC (direct methanol) type or DE-FC (direct ethanol) type with a polymer membrane are also suitable for providing the mobile generator according to the invention. In these fuel cells, liquid or vapor methanol or ethanol is used directly as an anode gas instead of the hydrogen, thus avoiding the hardware complexity for production of hydrogen. A further particular advantage is that, for example, methanol can be made available as fuel for the cell from commercially available replenishment installations; in contrast, safety standards which are physically complex to meet must first of all be complied with for hydrogen replenishment.

Finally, fuel cells of the SO-FC (solid oxide) type, with their internal reformation in the ceramic electrolyte, can directly (that is to say without any external reformation requirement) convert methane or even carbon monoxide (coal gas) into electricity in addition to the hydrogen. Furthermore, there is no need for a moisturizer for the cell in this case. It can be operated using alcohols or hydrocarbons (for example petrol, diesel, kerosene) via an external reformer. Its efficiency, which is very high in any case, is increased considerably further by pressure-boosted operation. This is of particular interest for operation of wide-body aircraft when parked even in front of the gates, because the conventional apron underground supply from the supply pillars which are permanently installed close to the building is often actually not designed for their power requirement.

In order to operate a PEM-FC with relatively complex alcohols or hydrocarbons, so-called shift stages are required in addition to the reformer, for conversion of carbon monoxide with water to carbon dioxide and hydrogen, as well as so-called PrOx (preferential oxidation) stages for oxidation of the remaining carbon monoxide to carbon dioxide, since the PEM-FC is damaged by carbon monoxide.

BRIEF DESCRIPTION OF THE DRAWINGS

Additional inventive developments, modifications and alternatives to the solution according to the invention are specified in the further claims and, with respect to their advantages as well, will become evident from the following description of one preferred exemplary embodiment of the invention. The single figure in the drawing shows a mobile generator of this type, equipped with a fuel cell, for supplying ground power to the on-board power supply system, in particular of a parked aircraft (not shown), not to scale and illustrated in a manner that is restricted to the equipment which is essential for operation.

DETAILED DESCRIPTION

Accordingly, the mobile generator 1 is essentially designed as a standardized trolley 2. The trolley may, for example, be a trolley similar to that which is already used as a trailer or a self-propelled vehicle for conventional diesel-generator-based ground power supplies. However, a standardized frame structure is more expedient, whose dimensions can be physically matched as required to the variable, current particular circumstances of the power-related equipment of a fuel cell 3, for example with regard to its replenishment cycles.

The trolley 2 is equipped not only with the fuel cell 3 itself but also with the active substances for its operation, specifically, typically, with cryogenic tanks 4 and 5 for liquid hydrogen as the fuel and for liquid oxygen as the oxidant (that is to say LH₂ and LOX) because of their high volumetric and gravimetric densities. The tank 5 for the oxidant may, as has already been mentioned, also be replaced by a compressor or by a turbocharger for environmental air, depending on the principle of operation of the fuel cell 3.

The installation and process components 6 which are taken into account as required in the lower area of the trolley 2 comprise, for example, valves, sensors, heat exchangers, moisturizers and dehumidifiers, as required for autonomous operation of the fuel cell 3 in the trolley 2.

On switching on (then for preheating of the cryogenic active substances) and later when shutting down for switching off, the power supply of the system of the fuel cell 3 is used as its own electrical energy store 7, preferably designed as a lithium-polymer rechargeable battery, which can be recharged from the fuel cell 3 during operation of the latter.

The DC voltage which is obtained in the fuel cell 3 from its chemical reaction energy and, possibly temporarily and additionally, power drawn from the electrical energy store 7 to cover a peak demand power level, is converted in a converter 8, in terms of type of power and amplitude, to the normal on-board power supply system voltages, typically 28 volts DC and 115 volts AC 400 Hz.

A control unit 9 with control and monitoring functions optimizes the power generation and output in terms of the electrical power which is fed into an on-board power supply system via docking interfaces 10. If the power demand is correspondingly high, a plurality of such generators 1 can also be connected to an on-board power supply system (not shown in the drawing) in parallel via these interfaces 10.

Even a trolley 2 just designed to the dimensions of the Atlas Standard (805 mm long, 302 mm wide and 1008 mm high) as used for aircraft galleys is sufficient to store the fuel supply to obtain about 30 kWh_(el) of electrical energy, with the fuel cell 3 being designed to produce approximately 33 kW_(el) of electrical power from 240 cells. The chemical energy required for this purpose is approximately 50 kWh_(ch), but, in the case of cryogenic storage, would then not be available or would not be available at all, the conventional diesel-powered electrodynamic generator is, according to the invention, replaced by a mobile generator 1 with an electrochemical cell 3 as the source of the electrical power for a temporary external feed to the on-board power supply system. The cell 3 may be a rechargeable lithium battery; however, it is preferably a fuel cell 3 with active-substance stores 4, 5 and also with all the other additional devices for its autonomous operation in a self-propelled or towed trolley 2.

LIST OF SYMBOLS

-   1 Generator -   2 Trolley -   3 Fuel cell -   4 H₂ tank (hydrogen) -   5 O₂ tank (oxygen), compressor or electrical turbocharger -   6 Installation components -   7 Auxiliary rechargeable battery (Li-ion) -   8 Voltage converter (DC/DC, DC/AC) -   9 Control and monitoring unit -   10 Docking interfaces for adaptor cable 

1. A mobile generator (1) for supplying ground power to the on-board power supply system in particular of a parked aircraft, wherein the mobile generator (1) includes a towed or self-propelled trolley (2) having at least one electrochemical cell (3) as a power source.
 2. The generator as claimed in claim 1, wherein the generator has at least one rechargeable battery as the power source (3).
 3. The generator as claimed in claim 2, wherein the power source (3) is selectively constituted of a lithium-based rechargeable battery; high-capacitance capacitors, or electrical energy storage units.
 4. The generator as claimed in claim 1, wherein the generator has a fuel cell (3) and all the devices for its autonomous operation located in the trolley (2).
 5. The generator as claimed in claim 4, wherein the fuel cell (3) for the generator is selectively operated with hydrogen, methanol or ethanol as fuel and with oxygen as an oxidant, as its active substances.
 6. The generator as claimed in claim 5, wherein the generator is equipped with cryogenic tanks (4, 5) for containing its active substances.
 7. The generator as claimed in claim 5, wherein there is utilized a compressor or an electrical turbocharger for supplying the oxygen, such as air oxygen, into the fuel cell (3).
 8. The generator as claimed in claim 5, wherein there are selectively employed gas cylinders, metal-hydride stores, carbon nanotubes, carbon nanofibers or nanocubes (so-called MOFs=Metal Organic Frameworks) for storing the hydrogen.
 9. The generator as claimed in claim 4, wherein said cell comprises a solid-oxide fuel cell (3).
 10. The generator as claimed in claim 4, wherein the generator is equipped with a reformer, and additionally with shift stages and PrOx stages for use of alcohols or hydrocarbons as a fuel.
 11. The generator as claimed in claim 3, wherein a chemical compound which is rich in hydrogen, selected from calcium hydride, sodium-boron hydride, amine borane, starch, formic acid or silanes is stored in tanks, and the hydrogen required for the fuel cell is produced therefrom by a reformer.
 12. The generator as claimed in claim 1, wherein the generator is equipped with a voltage converter (8) and with at least one docking interface (10). 